Fabric light control window covering

ABSTRACT

A fabric light control window covering in which fabric vanes are adhesively bonded between two sheer fabric sheets such that relative movement between the sheer fabric sheets in a direction perpendicular to the longitudinal direction of the fabric vanes changes the angle of the fabric vanes and, thus, controls the amount of light admitted through the shade. The vanes are bonded to the sheer fabric sheets in a manner which tends to bias the sheer fabric sheets together to the nonlight admitting position. Also, disclosed are methods and apparatus for manufacturing the above window covering. The method features linear application of adhesive to the vane material which provides for a uniform appearance in the finished product. A heat setting process and apparatus is disclosed in which the bonded layers of sheer fabrics and vanes are fed between belts over hot and cool surfaces, under uniform tension and pressure. This provides for heat setting of the layers of the window covering to a uniform temperature-size relationship without inducing wrinkles or distortion into the fabric during heat setting.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/602,998, filed Oct. 24, 1990 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to window coverings and, moreparticularly, to fabric window coverings provided with adjustable vanesfor controlling the amount of light passing therethrough. The presentinvention also includes methods and apparatus for producing such awindow covering.

Fabric window coverings are often preferred by consumers for a number oftheir features. The features most often considered desirable are thesofter appearance relative to traditional venetian blinds, the uniformappearance which they provide a window, and the insulating propertiesassociated with cellular fabric shades.

Cellular fabric shades offering these features are known in the art. Forexample, U.S. Pat. No. 4,450,027 to Colson discloses cellular windowcoverings which may be made of fabric or film materials. In the processdisclosed in the Colson patent, a flexible strip material is folded intoa continuous longitudinal tube and the longitudinal folds thus createdare permanently set by passing the tubing material around a heat settingwheel. Adhesive is applied along one side of the flattened tubularmaterial which is subsequently stacked by winding onto a rack havingflat surfaces. The winding in this manner presses the adhesive to thenext layer wound onto the rack to form a bonded unitary stack of closedtubular cells. When the ends are cut from the rack the stack may beexpanded and the permanently set creases provide a neat and uniformoutward appearance.

U.S. Pat. No. 4,732,630 to Schnebly discloses a modification to theColson process described above. In the Schnebly patent a hot-meltadhesive is applied to one side of the tubular material. After the flattubular strips have been stacked and cut, they are placed in an ovenunder pressure and the hot-melt adhesive is activated to bond the layerstogether.

Both of the above patents disclose window coverings which exhibit thedesirable features discussed to this point. However, window coverings ofthat type lack one feature which is often desired by consumers. Thatfeature is the ability to control the amount of light admitted throughthe window covering, similar to a traditional venetian blind. There havebeen some attempts to provide a fabric window covering with the abilityto control the amount of light entering the room. However, theseattempts have lacked one or more of the features discussed above andhave been less than successful.

U.S. Pat. No. 3,384,519 to Froget discloses one such attempt. The windowcovering disclosed therein consists of two cloth layers spaced apart bymovable parallel blades having each of their marginal edges heat-weldedto one of the movable cloth layers. With this window covering, relativemovement of the two cloth layers in a direction perpendicular to theblades changes the angle of the blade and thus controls the amount oflight admitted through the article. A number of undesirable features ofthe Froget window covering derive from the fact that it is constructedutilizing a heat-welding process. First, this limits the fabrics whichmay be utilized to thermoplastic materials. Also, heat-weldingnecessarily requires a melting of at least some of the fibers of thematerials bonded, thus providing an uneven outer appearance along theheat-welds and producing unwanted crimps or creases in the materials,which can result in fatigue failure. Further, heat-welding is arelatively slow process which may require six or more seconds to createa bond over an extended length. This is too slow for application in highvolume commercial production processes. Other drawbacks of the Frogetwindow covering are that heat welds are limited in strength, especiallyat elevated temperatures experienced by an insulating type shade placedadjacent a sunlit window; and the difficulty in achieving uniformlystraight heat welded joints over an extended length.

U.S Pat. No. 2,865,446 to Cole discloses a window covering in which along rectangular piece of fabric is doubled back upon itself and aplurality of pleated elements are placed between the folded over sheets.The pleated elements are an accordion-pleated fabric which extends whenthe two sides of the folded over fabric are moved relative to oneanother in a direction perpendicular to the accordion pleats. Such awindow covering does not provide a uniform appearance because theaccordion-pleated fabric located closer to the top of the windowcovering does not expand to the same extent as the fabric closer to thebottom of the window covering. Also, it is very difficult to ensure thatsuch accordion-pleated fabric returns to its desired position after eachexpansion.

The construction of Cole inherently creates an undesirable feature if awoven type sheer fabric is used for the folded over, long rectangularpiece of fabric. That undesirable feature is a moire effect orinterference pattern which would result when light is viewed through thefolded over fabric. The Froget window covering would also appear to havethis drawback because the embodiment shown in FIG. 8 of that patentappears to show front and back fabrics of the same material.

French Patent No. 1,309,194 discloses a curtain with variable opacity.In this curtain, screen or mesh parallel sides are provided withtiltable braids therebetween. The braids are said to be attached attheir edges to the sides, however, no means for attachment is specified.The drawings appear to indicate a hinged type attachment and thespecification ends by stating that the difficulties of construction aresubstantial.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a fabriclight control window covering comprising first and second parallel sheerfabric sides and a plurality of opaque or semi-opaque vanes extendingbetween the sheer fabric sides with the vanes being angularlycontrollable by relative movement of the sheer fabric sides.

Another object of the invention is to provide such a window coveringwhich has a neat and uniform construction and outer appearance in alldegrees of light control. In this respect a feature of the presentinvention is therefore adhesive bonding of the light control vanes tothe sheer fabric utilizing linear application of the adhesive and, thus,a high degree of controllability of the adhesive application process andbonding of the vane. Such a feature provides advantages other thansimply an improved outward appearance. The precisely uniformconstruction improves the operation of the blind by preventing warps ordistortions from developing over the life of the blind.

Another object of the invention is to provide such a blind whichoperates with a high degree of repeatability, that is, always returns tothe same appearance when closed. Thus, a feature of the presentinvention is attachment of the vanes to the sheer fabric sides such thatthe vanes tend to bias the window covering toward the minimum lightadmitting position. A further feature of the invention in this respectis a novel heat setting of the three layers together in order to providea uniform and wrinkle-free shade at any temperature in subsequent use.These features allow the window covering to maintain its original shapeand appearance even in the presence of temperature extremes encounteredin a window environment.

A further object of the present invention is to provide methods andapparatus capable of producing the above window covering. One of thefeatures of the present invention is adhesive bonding by means ofadhesive linearly applied on the vane material. Linear applicationensures a high degree of accuracy and provides uniform and straightadhesive lines. Another feature of the invention is the unique heatsetting process utilizing hot and cold rollers and tension belts or hotand cold flat plates and belts to uniformly press the sandwiched fabricsduring reheat setting and thus guarantee a wrinkle-free structure.

It is also an object of the present invention to provide such methodsand apparatus which are suitable for high volume commercial typeproduction. Features of the present invention which assist in thisrespect are adhesive bonding techniques which allow almost instantaneousbonding of the vane material and apparatus which allow for materialchanges without complete resetup.

Accordingly, a fabric light control window covering according to thepresent invention comprises a first sheer fabric sheet, a second sheerfabric sheet disposed parallel to the first sheet, and a plurality ofrelatively opaque fabric strips adhesively bonded transversely betweenthe sheet fabrics. Each strip has an edge portion bonded to the firstsheet and an opposite edge portion bonded to the second sheet in amanner tending to bias the first and second sheets together. The windowcovering according to the present invention is movable between a closedposition and an open position. The closed position is characterized by acentral portion of the fabric strips being substantially parallel to thefirst and second sheer fabric sheets with the strips themselves beingsubstantially planar. The open position is characterized by the centralportion of the fabric strips being substantially perpendicular to thefirst and second fabric sheets and to the bonded edge portions of thestrips themselves. Also, characteristic of this position is thatportions of the strips between the bonded edge portions and centralportions form smoothly curving surfaces which are free of creases orsharp fold. In an alternative embodiment, the central portions of thefabric strips are substantially flat and longitudinally extending hingeor flex points are provided parallel to the bonded edge portions.

According to a preferred embodiment of the invention the method formanufacturing such a window covering generally includes the followingsteps. A first line of hot-melt adhesive is applied to the narrow stripmaterial adjacent one edge on one side. A second line of hot-meltadhesive is applied to the narrow strip material adjacent the oppositeedge on the opposite side. The narrow strip material is then cut tolengths equal to the width of the wider sheer fabrics and the cutlengths are separated to provide a space between them sufficient toallow for a subsequent processing step. The first sheer fabric is fed ata constant rate longitudinally in a direction perpendicular to thelongitudinal direction of the cut strips. The first sheer fabric is alsofed over the cut strips in close proximity thereto. As the first sheerfabric is fed, a portion is preheated to a temperature sufficient toform a tack bond with the hot-melt adhesive. Then, while continuouslyfeeding the first sheer fabric at a constant rate, a portion of thefirst sheer fabric is stopped directly over one of the cut strips sothat the cut strip may be pressed and bonded to the first sheer fabricwithout smearing the adhesive. In order to move the bonded strips out ofthe way of the next strip, the stopped portion of the first sheer fabricis advanced at a speed greater than the constant feed rate, followed bya reversing of the direction of travel of the formerly stopped portionto position the first sheer fabric for application of the next cut stripin an overlaying relationship to the previously applied cut strip. Thesecond sheer fabric is then fed into mating contact with the cut stripswhich have been bonded to the first sheer fabric, thereby forming asandwich of three layers. Almost immediately after feeding the secondsheer fabric, the sandwich is heated under uniform pressure and tensionto melt and force the hot-melt adhesive into the sheer fabrics, and setthe layers of the sandwich at a uniform temperature-size relationship.Finally, the fabric sandwich is cooled under uniform pressure andtension, thereby permanently bonding the sheer fabrics to the cut stripswithout creating warps or wrinkles. The final, permanently bonded fabriccan then be cut to desired lateral widths and/or trimmed along thelateral edges thereof.

Apparatus according to the invention generally comprises means forperforming the above described method. In particular, the apparatusincludes an adhesive applicator means comprising a heating block formelting the hot-melt adhesive. The heating block contains a gear pumpwhich provides melted adhesive to nozzles at a rate proportional to thespeed of feeding of the strip material. The heating block also isdesigned to melt only a small portion of adhesive in order to preventyellowing while maintaining an adequate adhesive flow.

Included in the present invention is a means for positioning the firstsheer fabric in order to stop a portion for application of a cut stripand then reposition and stop the fabric before the application of thenext cut strip while maintaining a constant feed rate for the firstsheer fabric. This portion of the apparatus comprises two dancer rollersaround which the first sheer fabric runs. The dancer rollers are mountedon shafts which form the pivot points of a linkage around its frame. Thelinkage causes the dancer rollers to act in concert and the timing ofthe rotation of the linkage is controlled by an appropriately shaped cammember.

A heat setting means is provided in which the sandwiched layers of thewindow covering pass between first and second adjacent endless belts.The belts each run across hot and cool surfaces to successively heat andcool the window covering. In one embodiment, the hot and cool surfacesare rollers and tension induced in the belts causes a pressure to beexerted on the sandwiched layers, thus maintaining the layers underconstant and uniform pressure at a tension significantly less than thetension induced in the endless belts. In another embodiment, the hot andcool surfaces are flat plates disposed opposite air plenums and thepressure exerted on the sandwiched layers is due to the biasing of thebelts toward the flat plates by pressurized air supplied to the airplenums. Alternatively, the hot and cool surfaces may be pairs ofoppositely disposed flat plates biased against the belts. Heat settingin these manners allows the sandwiched layers to be set to a uniformtemperature and size relationship to prevent distortions in subsequentuse.

Also, included in a preferred embodiment of the invention is a heatsetting means wherein the first endless belt passes around a hot rollerand the second endless belt passes around a cool roller. The location ofthe belts and rollers is arranged such that the second endless belt alsopasses around the hot roller outside of the first endless belt and thefirst endless belt passes around the cool roller for short distanceoutside of the second endless belt. With this arrangement the sandwichedlayers of the window covering may be passed between the two belts,around the hot and cool rollers.

A hot knife cutting assembly is preferably provided to cut the finalfabric to desired lateral widths and/or to trim the lateral edges of thefinal fabric. The hot knife cutting assembly operates such that thethree layer sandwich fabric is cut cleanly, without any heat sealing ofthe lateral edges of the individual fabric layers to one another.

BRIEF DESCRIPTION OF THE DRAWING

The features and advantages of the present invention will be morereadily apparent from the following detailed description of thepreferred embodiments, illustrated in the drawing figures wherein:

FIG. 1 is a front elevation view of a preferred embodiment of theapparatus according to the present invention;

FIG. 2 is a left side elevation view of the apparatus shown in FIG. 1;

FIG. 3 is a diagrammatic view generally representing the apparatus as itwould appear viewed through line 3--3 in FIG. 1;

FIG. 4 is an enlarged perspective view of the vane material of thepresent invention as viewed through line 4--4 in FIG. 1;

FIG. 5 is an enlarged perspective view of the sheer fabric with attachedvane material at box 5 in FIG. 3;

FIG. 6 is a perspective end view of a fabric light control windowcovering according to the present invention;

FIG. 7 is a perspective end view of the window covering according to thepresent invention illustrating a possible method of deployment;

FIG. 8 is a diagrammatic illustration of a preferred embodiment of thecutting means of the present invention;

FIG. 9 is a diagrammatic illustration of an alternate embodiment of theheat setting apparatus according to the invention;

FIG. 10 is a diagrammatic illustration of a further alternate embodimentof the heat setting method and apparatus of the invention;

FIG. 11 is a side view of a hot knife cutting assembly according to theinvention;

FIG. 12 is a side view of a second embodiment of a fabric light controlwindow covering according to the present invention;

FIG. 13 is an end view of a vane material for the fabric light controlwindow covering in FIG. 12; and

FIG. 14 is a diagrammatic, cross-sectional illustration of still anotheralternate embodiment of the heat setting method and apparatus of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawing and, in particular, first to FIG. 1, the methodand apparatus according to the present invention may be explained ingreater detail. Vane material 10 is provided as a continuous strip offlexible material from supply roll 12. Vane material 10 first passesaround idler roller 13 mounted on frame 14. The vane material thenenters adhesive applicator assembly 20, where adhesive nozzles 21 applya thin line 16 of hot-melt adhesive to each side of the vane material 10(see FIG. 4). While the apparatus is explained below in connection withhot-melt adhesive, it should be readily appreciated that the sameprinciples are generally applicable to other types of liquid adhesives.

In assembly 20 vane material 10 first passes around alignment roller 22which is provided with raised edges in order to ensure proper alignmentof the material. Vane material 10 next passes around backup roller 23over which nozzle 21 is disposed. Backup roller 23 is mounted on arm 24and shaft 26 which pivots in bearing 25 to allow for adjustment of thespacing between the glue nozzle 21 and vane material 10 on backup roller23. Preferably, the spacing is adjusted to provide a flat glue line asshown in FIG. 4. The flat profile of the adhesive lines provides greatercontrol of the amount of adhesive applied and the degree of flow whensubsequently squeezed between two materials. With a two inch wide vanematerial 10, the dimensions of the adhesive lines are preferably about aheight of 0.003 inches and a width of 0.60 inches.

Driven roller 27 is provided to assist in feeding the vane material andis positioned to ensure that vane material 10 has sufficient contactwith backup roller 23. By passing vane material 10 under stationarynozzle 21, the adhesive lines are applied due to the linear motion ofthe vane material 10 in its longitudinal direction. In this manner greatprecision can be achieved in the application of the adhesive lines.

As illustrated in FIG. 4, adhesive line 16a is disposed on vane material10 adjacent one edge and on one side of the material. A second adhesive16b is disposed adjacent the opposite edge on the opposite side of thematerial. The second adhesive line 16b is placed on vane material 10 byutilizing the same components as just described arranged in a mirrorimage configuration and by doubling vane material 10 back over itselfaround the second backup roller 23.

In a preferred embodiment of the present invention, the adhesive used isa copolyester hot-melt adhesive. This adhesive melts and flows at about350° F. and provides excellent strength over the temperature range towhich the window covering will be exposed in use. It also provides atack bond at slightly lower temperatures around 220° F. which is usefulin subsequent steps as described below.

This type of adhesive however does have the undesirable characteristicof yellowing when heated and maintained in a melted state for extendedperiods of time. In order to prevent yellowing, it is necessary to heatonly a small amount of adhesive at a time. The present inventionprovides a novel system of adhesive application which eliminates thisproblem. Hot-melt adhesive in the form of pellets is placed in hopper30. The pellets drop into caulking cartridge 32 which is provided with apneumatic piston 34 that forces the pellets into heating block 35.Electric heating elements 36 heat heating block 35 to melt a smallamount of adhesive just before it is forced into a metering gear pumpwhich pumps the adhesive into nozzles 21. With this arrangement aslittle as four ounces of adhesive is melted at one time.

A gear pump, preferably a positive displacement pump, is disposed withinheating block 35 to pump the melted adhesive to nozzles 21. The gearpump is powered proportionally to the vane material 10 feed speed suchthat the amount of glue deposited on the vane material 10 remainsconstant at whatever speed the vane material is fed.

After leaving the adhesive applicator assembly 20 vane material 10, withapplied adhesive lines 16a, 16b, passes around idler rollers 33 and 37.The vane material then travels around alignment roller 38 which hasraised edges to align the vane material and a further idler roller 39.Vane material 10 then travels into cutter assembly 40.

Cutter assembly 40 is shown schematically in greater detail in FIG. 8.In the cutter assembly, vane material 10 first passes around analignment roller 41. Alignment roller 41 has raised edges similar to theother alignment rollers in order to guarantee the side-to-side alignmentof vane material 10. The vane material then passes between backup roller42 and nip roller 44. Nip roller 44 is mounted on a pivotable springbiased arm 43 in order to maintain a constant pressure against thebackup roller 42 and prevent slippage of vane material 10. Backup roller42 is also a driven roller which pulls the vane material through theapparatus. Adjacent to backup roller 42 is cutting roller 49. Blade 50is disposed on the circumference of cutting roller 49 parallel to theroller axis. Cutting roller 49 and backup roller 42 are spaced apart adistance sufficient to prevent blade 50 from cutting vane material 10 oneach rotation of the rollers.

Cutting roller 49 is rotatably mounted on bracket 48 which pivots onshaft 51. After the desired length of fabric is fed around backup roller42, pneumatic cylinder 46, mounted on bracket 47 and acting throughlinkage 45, causes bracket 48 to pivot to the left so that blade 50contacts and cuts material 10 to form individual vane strips 10a.Linkage 45 comprises a clevis 52 attached to the end of the cylinderpiston. Three connecting rods 53, 54 and 58 are joined at pivot point 56and are pivotably connected at clevis 52, cutter assembly frame 57 andbracket 48, respectively. The downward motion exerted by cylinder 46causes pivot point 56 to move down and thus pivots bracket 48 to theleft around shaft 51.

Pneumatic cylinder 46 is controlled by a pneumatic valve (not shown)cooperating with the backup roller shaft. After the number of rotationsof backup roller 42 corresponding to the desired length of vane material10, the pneumatic valve opens to actuate pneumatic cylinder 46 and thusmove blade 50 to the cutting position. Backup roller 42 and cuttingroller 49 are both driven rollers travelling at the same speed in orderto prevent a scraping action of blade 50 along backup roller 42.

In an alternate embodiment, nip roller 44 and biased arm 43 areeliminated. Instead, cutting roller 49 is surrounded by a squishablerubber liner having an outer diameter slightly greater than the radialextension of blade 50 and contacting backup roller 42. The contactbetween the cutting roller rubber liner and backup roller 42 creates anip for pulling fabric through the apparatus. When air cylinder 46causes bracket 48 to move slightly to the left to cut the vane material,the rubber liner is compressed against backup roller 42 to exposecutting blade 50 and thus cut vane material 10.

After vane material 10 passes around backup roller 42 it falls ontovacuum belt 62 which is part of vacuum separator assembly 60. In FIG. 8vane material 10 is shown slightly above belt 62 in order to clearlydistinguish the two parts, in practice material 10 is pulled againstbelt 62. Vacuum separator assembly separates the cut strips 10a of vanematerial in order to provide a sufficient distance between the strips toallow time for subsequent processing steps performed on the individualstrips 10a. Vacuum belt 62 is provided with holes which are best seen inFIGS. and 3. Vacuum belt 62 travels around drive wheel 61, idler wheeland idler wheel 70 which is mounted on screw tension adjustment 67.Screw tension adjustment 67 allows the tension in vacuum belt to beadjusted by turning screws 67a. Vacuum belt 62 is supported along itstop run 62a by hollow frame 64. The space within hollow frame 64 isevacuated by vacuum hoses 69, thus causing a suction through the holesof vacuum belt 62. This suction pulls the vane material against vacuumbelt 62 as it comes off backup roller 42.

In order to provide the spacing between the cut strips 10a of vanematerial, vacuum belt 62 travels approximately twice as fast as thelinear feed speed of vane material 10. Thus, as the uncut vane material10 passes backup roller 42, it is pulled against vacuum belt 62 by thesuction action. However, because it is moving at a slower speed, uncutvane material 10 slides along vacuum belt 62. As soon as vane material10 is cut by blade 50, it is separated from the uncut vane material 10due to the increased speed of the vacuum belt 62. Nip roller 65 pressesagainst vacuum belt 62 and is located a distance from the point ofcontact between blade 50 and backup roller 42 slightly less than thedesired length of individual cut strips 10a. Pneumatic cylinder 66 actson arm 68 on which nip roller 65 is mounted in order to press nip roller65 against vacuum belt 62. The actuation of air cylinder 66 is timed tocorrespond to that of pneumatic cylinder 46 such that at the precisemoment vane material 10 is cut, nip roller 65 presses cut strip 10aagainst vacuum belt 62 to ensure its separation from the uncut vanematerial. Vacuum belt 62 moves the cut vane strips 10a to a positiondirectly under first sheer fabric 72.

The cutting assembly 40 and separator assembly 60 allow for successfulhandling of relatively soft fabrics for the vanes 10a. This is asignificant advantage over the prior art because soft fabrics provide amore pleasing appearance in the final product.

Referring to FIG. 3, first sheer fabric 72 is provided from supplyroller 74 and fed around idler 75, dancer roller 76 and preheat shoe 78.The cut vane 10a is carried beneath a portion of first sheer fabric 72which is resting against preheat shoe 78. Preheat shoe 78 heats firstsheer fabric 72 to approximately 220° F. First sheer fabric 72 is fedwith its longitudinal direction perpendicular to the longitudinaldirection of the vane 10a. The width of first sheer fabric 72corresponds substantially to the cut length of vane 10a.

When vane 10a reaches alignment with the opposite edge of first sheerfabric 72, photo eye 80 senses the end of vane 10a and activates kickerbar 82. Kicker bar 82 is located on one side of vacuum belt 62 anddirectly below adhesive line 16a. Kicker bar 82 pushes the front edge ofvane 10a upwards and presses adhesive line 16a between vane 10a and thepreheated first sheer fabric 72. The combination of heat and pressurecreates a tack bond between vane 10a and first sheer fabric 72, thusholding vane 10a in place on first sheer fabric 72. Kicker bar 82 thenretracts downwards and out of the way of the next vane. Kicker bar 82 ismounted on a number of pneumatic cylinders 83 which provide the pressingforce and accomplish the tack bond cycle within a span of aboutone-tenth of a second. First sheer fabric 72 with tack bonded vanes 10a,as shown in FIG. 3, then moves around dancer roller 84 and idler roller86 into heat setting assembly 100.

In the window covering according to the present invention it ispreferred to have the vanes slightly overlapping in the closed positionin order to fully block the passage of light. This overlap requirementsomewhat complicates the production of the window covering in order toprevent the subsequently attached vane from being adhered to theprevious vane instead of the sheer fabric. In the present invention,dancer rollers 76 and 84 continuously reposition first sheer fabric 72to solve this problem. The sheer fabric in the present invention is fedat a continuous rate and pulled through the apparatus by the heatsetting assembly 100. In order to facilitate understanding of the methodand apparatus for positioning first sheer fabric 72, the description ismade with reference to a two inch wide vane material 10. It should bereadily appreciated that this is intended to in no way limit the presentinvention. Other vane material widths may be used with simpleadjustments, apparent to those skilled in the art based on thedisclosure contained herein.

With a two inch vane material, the overlap of the vanes is preferablyabout 1/4 inch. Therefore, the first sheer fabric 72 is advanced a totalof 13/4 inches for each vane 10a applied. In order to control andposition first sheer fabric 72, the first sheer fabric 72 runs arounddancer rollers 76 and 84. After a vane 10a has been applied, dancerroller 76 moves downward and dancer roller 84 moves to the left as shownin FIG. 3. This causes first sheer fabric 72 to be moved forward a totalof 23/4 inches at a rate faster than that at which first sheer fabric 72is actually being fed. The forward movement of 23/4 inches allows thetack bonded vane 10a to move completely out of the way of the next vaneto be applied. From this point, first sheer fabric 72 is moved backwardone inch by the dancer rollers in order to assume the proper position ofa total of 13/4 inches advancement. This positions the first sheerfabric 72 in place for the next vane 10a to be applied.

As the backward motion occurs, air jets 79 blow a jet of air throughfirst sheer fabric 72 on to applied vane 10a to force it out of the wayof kicker bar 82. A number of air jets 79 may be positioned along thewidth of first sheer fabric 72 just after kicker bar 82. Air jets 79 mayprovide a continuing airflow or may be timed to blow only during thebackward motion of the dancers.

In order to maintain first sheer fabric 72 in a stationary positionwhile the next vane 10a is applied, dancer rollers 84 and 76 continue tomove back slowly so as to exactly counter the effect of the forward pullof heat setting assembly 100. Thus, first sheer fabric 72 between dancerrollers 76 and 84 remains briefly stationary. This prevents adhesiveline 16a from being smeared when vane 10a is applied to first sheerfabric 72 and also allows first sheer fabric 72 to become sufficientlypreheated by remaining stationary on the preheat shoe 78. Once kickerbar 82 tack bonds the next vane 10a to first sheer fabric 72 thepositioning process repeats.

In a preferred embodiment of the present invention a single motor drivesystem is utilized to power adhesive applicator assembly 20, cutterassembly 40, vacuum separator assembly 60 and heat setting assembly 100.Dancer rollers 84 and 76 are also powered by this drive system. Dancerroller 76 is mounted on arms 89 which in turn are mounted on shaft 88.Similarly, dancer roller 84 is mounted on arms 85 which in turn aremounted on shaft 87. Shafts 87 and 88 extend through frame 14 as shownin FIGS. 1 and 2. Shafts 87 and 88 are linked together by arms 90 and 91and connecting rod 92 which, together with frame 14 form a linkage. Arm91 rides on cam 93 which is rotated by a shaft linked to the singlemotor drive system. Arm 91 is maintained in contact with cam 93 byextension spring 94. Cam 93 is shaped to provide the motion of dancerrollers 76 and 84 just described.

As can be seen in FIG. 1, vacuum belt 62 extends beyond frame 14 at theleft end of the apparatus. This allows for fast and easy changes of thevane material 10. When a new vane material is placed on a supply roller12, its leading edge may be simply taped to the trailing edge of thelast vane material. Then, when the cut strip containing the taped spliceapproaches first sheer fabric 72, kicker bar 82 and the sheer fabricfeed may be temporarily deactivated to allow the spliced portion of vanematerial to exit at the left side of the apparatus. When clean cutstrips 10a of vane material begin to exit at the left side, the sheerfabric feed and kicker bar 82 are reactivated. This allows quick changesof vane material without introducing flaws into the final product orrequiring lengthy set up times.

Referring again to FIG. 3 the remaining steps of the process may beexplained. First sheer fabric 72 which passes around idler roller 86 hasvanes 10a tack bonded thereto in their final spaced relationship. Secondsheer fabric 96 is fed from supply roller 97 around idler roller 98 andlaid up against first sheer fabric 72 with tack bonded vanes 10a. Thethree-layer sandwich of first sheer fabric 72, vanes 10a and secondsheer fabric 96 travels over idler 101, around heating roller 102 tocooling roller 104 and from there exits the apparatus as a finishedfabric 103. Heating roller 102 is maintained at a temperature ofapproximately 350° F. At this temperature hot melt adhesive lines 16a,16b are melted to form a permanent bond between the sheer fabrics 72, 96and vanes 10a. Cooling roller 104 is maintained at a temperature ofapproximately 120° F. and sets the hot-melt adhesive bonds.

In addition to providing an almost instant bond of high strength, theheat setting assembly provides a second function of equal importance. Byrunning the three layers together around heating roller 102 at atemperature of 350° F., the sheer fabrics and vane material are actuallyheat set to their new size and configuration at a uniformtemperature-size relationship. The fabrics will thus hold this new sizerelationship with respect to one another unless subjected again to atemperature of 350° F. or greater. The temperatures which normally wouldbe experienced by this type of window covering in use generally do notexceed a 180° F. Thus, the window covering according to the presentinvention will remain wrinkle-free at any normal use temperatures.

Additionally, the heat setting procedure allows for the use of fabricswhich have not previously been heat set. Most fabrics are run through aheat setting process which sets the fibers and locks them to size inorder to prevent shrinkage when subjected to heat in their normalapplications. The heat setting apparatus of the present invention allowsthis preheat setting of individual fabrics to be eliminated, thus savingtime and money in the fabric processing.

The present invention provides a further novel feature in order toensure that a wrinkle-free final product emerges from heat settingassembly 100. This feature is the use of endless tension belts 106 and108, respectively. First belt 106 travels around heating roller 102 andidler 110 mounted on shaft 111. Second belt 108 travels around coolingroller 104, idler 112, mounted on shaft 114, and idler 101. Second belt108 also travels around heating roller 102 outside of first belt 106.Similarly, first belt 106 travels for a short distance around coolingroller 104 outside of second belt 108. The three-layer fabric sandwichis pressed between the first and second belts 106, 108 as it passesaround heating and cooling rollers 102, 104. The first and second belts106, 108 are maintained at a much greater tension than the sandwich ofsheer fabrics 72, 96 and vanes 10a as it passes therebetween. Thetension in the belts has the effect of pressing together the beltsaround heating and cooling rollers 102, 104. This uniformly presses thefinished fabric 103 as it is heat set and cooled, thus furthereliminating the possibility for a wrinkled or warped final product. In apreferred embodiment, first and second belts 106, 108 arepolytetrafluoroethylene (TEFLON) coated fiberglass belts which have therequired strength and exhibit the release characteristics ofpolytetrafluoroethylene.

Referring to FIG. 2, the tensioning of belts 106 and 108 is controlledby pneumatic cylinders 120 and 122, provided in pairs on both sides offrame 14. Pneumatic cylinders 120 act on shaft 114 which carries idler112 and thus control the tension in cooling belt 108. Pneumaticcylinders 122 act on shaft 111 on which idler 110 is mounted and thuscontrol the tension in heating belt 106. Both of cylinders 120 can beseen in FIG. 1. Slotted arms 121 and 123 ensure alignment of shafts 114and 111, respectively. Air supply to the cylinders is controlled byregulators 128 and 129 The unwind tension of sheer fabric supply rollers74 and 97 is controlled by pneumatic brakes 124 and 125, which areregulated by regulators 126 and 127, respectively. The pneumatic brakesand regulators allow the tension in the sheer fabrics to be preciselycontrolled during the steps of bonding the vanes and heat setting thelayers together.

The rotation of heating and cooling rollers 102, 104 is linked togetherby geared wheels 132 and 134 which are in turn driven by gears 136 and138 linked to the drive system. Heating roller 102 may be heated byelectric heating elements disposed around the internal diameter of theroller which is preferably formed as a hollow aluminum cylinder. Coolingroller 104, also preferably formed as a hollow aluminum cylinder, may becooled by forced air convection or in larger rollers by liquid coolingpassages formed in the roller.

FIGS. 9, 10 and 14 illustrate alternative embodiments of the heatsetting apparatus according to the present invention. In FIG. 9, firstand second belts 106a and 108a are carried by rollers 115a and 110a androllers 113a and 114a, respectively. Tension in belts 106a and 108a maybe adjusted by the moving shafts 111a and 114a in the same manner asshafts 111 and 114, explained above. Second sheer fabric 96 is againsandwiched with first sheer fabric 72 having tack bonded vanes 10a. Thesandwiched layers then run between belts 106a and 108a. Heating isprovided by hot plates 102a and cooling by cool plates 104a disposedinside each of the belts. The plates are biased against the belts andsandwiched layers by springs 116 to ensure a uniform pressure on thesandwiched layers.

In the embodiment of FIG. 10 belts 106a and 108a are arranged generallyas shown in FIG. 9. However, instead of hot plates 102a a plurality ofhot rollers 102b are employed. Hot rollers 102b are disposed inside eachbelt 106a with the axes of the upper set of rollers offset between theaxes of the lower set of rollers. The axes of the upper and lower setsare also located slightly closer together than the diameter of therollers thus providing a slight wrap of the belts around each roller.The wrap around each roller creates a uniform pressure on the sandwichedlayers between belts 106a and 108a when tension is applied to the belts.In a preferred embodiment the rollers are positioned such that the beltswrap around an arc of approximately 20°. Rollers arranged in the samemanner as hot rollers 102b may be used as cooling rollers or coolingplates 104a may be employed.

In the embodiment of FIG. 14, first and second belts 106a and 108a arearranged generally as shown in FIG. 9. However, instead of two hotplates 102a and two cool plates 104a, only one hot plate 102c and onecool plate 104c disposed within endless belt 108a are employed. The hotplate 102c includes an air chamber 180 and a plurality of air bleedholes 182 are formed through hot plate 102c. The air bleed holes 182provide fluid communication through the hot plate 102c between the airchamber 180 and the upper surface of hot plate 102c. Similarly, coolplate 104c includes an air chamber 184 and a plurality of air bleedholes 186. Air plenums 188, 190 are disposed within endless belt 106aand are positioned opposite the hot plate 102c and the cool plate 104c,respectively. Each of the air plenums 188, 190 is provided with flexibleseals 198 around the lower edge thereof adjacent endless belt 106a.Preferably, the hot plate 102c and the cool plate 104c are wider thanthe belts 106a, 108a and the air plenums 188, 190 are narrower than theplates and the belts.

Air is supplied to air plenum 188 and air chamber 180 of the hot plate102a by hot air blower 192. More particularly, hot air blower 192supplies air at a pressure of about 3 to 4 psi and a temperature ofabout 350° to 400° F. to air plenum 188 through conduit 193 and to airchamber 180 through conduit 194. Hot plate 102c is also heated to atemperature of about 350° by suitable means. Air is supplied to airplenum 190 and air chamber 184 of cool plate 104c by cool air blower195. Air at a pressure of about 3 to 4 psi and ambient temperature issupplied by cool air blower 195 through conduit 196 to air chamber 184and through conduit 197 to air plenum 190. Cool plate 104c is cooled toa temperature of about 120° F. or lower, by suitable means such as watercooling.

The air pressure in the air plenums 188, 190 pushes or biases the belts106a, 108a, and the fabric sandwich 103 therebetween, toward the hotplate 102c and the cool plate 104c. In contrast to the embodiments ofFIGS. 3, 9 and 10, in the embodiment of FIG. 14 the tension in the belts106a, 108a is not critical. In this embodiment, the pressure applied tothe fabric sandwich 103 between the belts 106a, 108a is created by airpressure instead of tension. The 3 to 4 psi of air introduced into theair plenums 188, 190 pushes the belts 106a, 108a and the fabric sandwich103 against the hot plate 102c and the cool plate 104c, respectively.This uniformly presses the finished fabric 103 as it is heat set andcooled. Pressurized air flowing through the air bleed holes provided inthe hot plate 102c and the cool plate 104c lifts the belt 108a off thehot and cool plates, preferably a few thousandths of an inch, tominimize friction between the belt 108a and the plates to ensure uniformheating and cooling of the fabric sandwich 103.

After the finished fabric 103 exits the apparatus as shown in FIG. 3,the finished fabric 103 can be wound up in a roll for storage andsubsequent processing into a finished window covering, or the finishedfabric 103 can be immediately transported to trim the lateral edges ofthe finished fabric 103 and/or to cut the finished fabric 103 intodesired lateral widths. A suitable hot knife cutting assembly is shownin FIG. 11. The hot knife cutting assembly 300 comprises a movingcarriage 302 slidably or movably mounted on carriage rails 304. A hotwheel knife cutter 306 is rotatably mounted on the moving carriage 302and rotates in the direction indicated by arrow 308. A shoe 312 carriedby the moving carriage 302 holds the finished fabric 103 flat on thetable or support 314 until the fabric 103 is cut by the rotating hotwheel knife 306. Depending upon the material of the first sheer fabric,the second sheer fabric and vanes of the finished fabric 103, it may bepossible to carefully control the temperature of the hot wheel knife 306to prevent sealing of the lateral, cut edges of the three layers of thefinished fabric 103 to one another due to the heat of the hot wheelknife 306. However, preferably, an air jet 310 connected to an airsupply (not illustrated) is mounted on the moving carriage 302. Airsupplied through the air jet 310 blows onto the edge of the cut fabric103 immediately after the cutting, and air from the air jet 310 liftsand opens the lateral edges of the fabric 103 to prevent the edges ofthe fabric from sealing together. Instead of the air jet 310, othersuitable means for lifting and opening the finished fabric 103 along thecut edge thereof may be carried by the moving carriage 302 toimmediately effect opening of the finished fabric immediately after itis cut by the hot wheel knife 316. For example, mechanical opening meanscould be carried by the moving carriage to effect this opening.

The hot knife cutting assembly 300 may be employed to cut the finishedfabric 103 immediately after the finished fabric 103 has been produced,and prior to winding the finished fabric 103 into a roll for storage.Alternatively, the finished fabric 103 may be wound for storage andthen, at a subsequent time or a different physical location, thefinished fabric 103 from the storage roll can be cut using the hot knifecutting assembly 300.

FIGS. 6 and 7 illustrate a fabric light control window coveringaccording to the present invention. FIG. 6 illustrates the windowcovering in a fully open, light admitting position. In this position,each vane 10a has a central portion 140 which is substantiallyperpendicular to first and second sheer fabrics 72, 96. Edge portions142 of the vane 10a, which are bonded to the sheer fabrics are connectedto central portion 140 by a portion 141 having a smoothly curving shapewhereby the vane in cross section has reverse curves and is generallyS-shaped. The adhesive bonding process of the present invention allowsportion 141 to be formed without creases or sharp folds. The smoothlycurved nature of this portion, in the fully open position, allows thevane to retain its resiliency and thus tends to bias the sheer fabricsinto a closed or drawn together position. This ensures that the windowcovering does not lose its shape over time from repeated opening andclosing. Furthermore, creases along vanes 10a can develop into failurepoints due to repeated bending inherent in the opening an closing of thewindow covering.

FIG. 7 illustrates a possible method of deployment of a light controlwindow covering according to the present invention. The window covering150 is mounted on a head roller 152. The bottom of the first sheerfabric 72 may be provided with decorative stiffener 154. Second sheerfabric 96 is weighted by weight 153. Rotation of head roller 152 causesrelative movement between first and second sheer fabrics 72, 96 in avertical direction and thus an angular change in the orientation ofvanes 10a to let in or block out light as desired. First sheer fabric 72need not be weighted because of the tendency to close imparted by thebiasing effect of vanes 10a.

FIGS. 6 and 7 also illustrate the novel technique employed in thepresent invention for avoiding the appearance of a moire effect inwindow coverings of this type. With such window coverings, sheer wovenfabrics having small interstices between the fibers provide a pleasantand desirable appearance for the first and second sheer fabrics 72, 96.However, when the same or very similar material of this type is used forthe first and second sheer fabrics, a moire pattern is created by thefabrics when viewed in overlaying relationship. This moire effect iseliminated in the present invention by providing first and second sheerwoven or knit fabrics of materials having differently sized, shapedand/or oriented interstices. According to the present invention, themoire effect is also avoided by using a nonwoven sheer material as oneor both of the first and second fabrics or by using a transparentplastic material as one or both of the first and second fabrics.

To avoid the undesirable moire effect when the first and second sheerfabrics of woven or knit material are viewed in overlaying relation inthe window covering of the present invention, the first and second sheerfabrics must have different appearances when the sheer panels are viewedalong an axis perpendicular to the plane of the first sheer fabric 72and perpendicular to the plane of the second sheer fabric 96. Therequired difference in appearance between the first sheer fabric 72 andthe second sheer fabric 96 can be achieved in several different ways.

The first sheer fabric 72 can be a woven or knit fabric havinginterstices of one shape and the second sheer fabric can be a woven orknit material having interstices of a second shape. In one suchembodiment shown in FIG. 7, a woven fabric employing fibers formingsmall square interstices is used as the second sheer fabric 96. Amaterial used for the first sheer fabric 72 may have fibers forminginterstices which are smaller, the same size or larger than those of thesecond sheer fabric 96. However, the fibers of the first sheer fabric 72form interstices which are positioned as diamonds with respect to thesecond sheer fabric 96. With this relationship between first and secondsheer fabrics, the appearance of a moire pattern can be avoided.

In another embodiment, the first sheer fabric 72 can be a woven or knitfabric having interstices of one shape and size and the second sheerfabric 96 can be a woven or knit fabric having interstices of the sameshape as the first sheer fabric but of a different size. In this secondembodiment, shown in FIG. 6, the moire pattern may be avoided byproviding a second sheer fabric 96 which has interstices which aresmaller than those of first sheer fabric 72 without regard to therelative orientation or shape of the interstices. This also prevents theoccurrence of interference leading to a moire effect. In practice, thefirst and second fabrics are selected so that the width of theinterstices of the first fabric is far greater than the width of theinterstices of the second fabric, thereby avoiding the moire effect.

It is also possible to use the same woven fabric for both the first andsecond sheer fabrics 72, 96, provided that the woven fabric is orienteddifferently in the two sheer fabrics 72, 96 in order to provide therequired difference in appearance. For example, with reference to FIG.7, the woven fabric of second sheer fabric 96 has square interstices.The same woven fabric having square interstices can be used as the wovenfabric of the first sheer fabric 72 by changing the orientation of thewoven fabric by 45° to provide the diamond shaped interstices of thefirst sheer fabric 72. When the same woven fabric is used for both thefirst and second sheer fabrics 72, 96, the fabric for one of the sheerfabrics is cut on the bias so that the orientation of the interstices ofthat fabric is changed by an angular amount, e.g. roughly 45° or 90°,sufficient to provide the required difference in appearance when thefirst and second sheer fabrics 72, 96 are viewed along an axisperpendicular to the plane of both.

It is also possible to avoid the moire effect and provide the requireddifference in appearance by using a nonwoven sheer material, such as aplastic material, for one of the sheer fabrics and a woven sheermaterial for the other of the sheer fabrics of the window covering.Alternatively, nonwoven sheer materials, such as the same or differentplastic materials, can be used for both the first and second sheerfabrics. A transparent plastic material can also be used as the firstand/or second fabric. The use of a transparent material as at least oneof the first and second fabrics also avoids the moire effect.

In another embodiment of the present invention, the second sheer fabric96 is replaced by a series of sheer fabric strips or a series ofstrings. A window covering of this embodiment can be made by the sameprocess and apparatus as described above, however a series of parallelsheer fabric strips or parallel strings are fed to the apparatus from anappropriate supply roll instead of the second sheer fabric 96. The useof a series of strings or sheer fabric strips in place of the secondsheer fabric 96 provides a more "see-through" effect when the windowcovering is in the open position. However, because the overlappingconfiguration of the vanes is the same as that of a window coveringhaving a second sheer fabric 96, in the closed position a windowcovering comprising a plurality of strings or sheer fabric stripsprovides the same light blocking effect.

To achieve the gently curved structure of the vanes 10a shown in FIG. 6,the vane material must have a certain degree of softness. As a generalprinciple, the wider the vanes 10a, the stiffer the vane material canbe. However, since a broad range of vane widths may be employed inwindow coverings in accordance with the present invention, it isdifficult to precisely define an acceptable softness or stiffness rangefor the vane material.

A simple and effective physical test has been devised to determinewhether a particular fabric is suitable for vanes having a specific vanewidth. The fabric being tested is allowed to hang over the edge of atable such that the distance from the edge of the fabric to the tabletop equals the desired vane width. If this length of fabric hangssubstantially vertically, then it has sufficient softness for a vane ofthat vane width. For example, if a fabric is being tested for use as a2" wide vane, the edge of the fabric is extended 2" beyond the edge ofthe table. If the extended 2" of the fabric hangs substantiallyvertically from the table edge, it is suitable for use as a 2" wide vanematerial in the structure shown in FIG. 6. If the extended 2" of thefabric does not hang substantially vertically, the fabric is too stiffto produce 2" wide vanes having the gently curved appearance of FIG. 6.

Stiffer fabrics, i.e., those which do not hang substantially verticallyover a table edge at the length of the desired vane width, can also beused as the vane material. However, if a stiffer fabric is used for thevanes, longitudinally extending hinge or flex points must be providedalong the edges of the vanes. The use of a stiffer fabric provided withhinge points produces a window covering having a somewhat differentappearance than the window covering shown in FIG. 6. This secondembodiment of a window covering is shown in FIGS. 12 and 13. As seen inFIG. 12, vanes 210a have a straighter appearance and have a sharp bendat the hinge points 212 and 214, rather than a gently curving portion141 as shown in FIG. 6. The hinge points 212, 214 are provided byscore-compressing a stiff vane material, parallel to the longitudinaledges of the vane material. The score-compressed lines formed in thestiff vane material are spaced apart from the longitudinal edge of thevane material a distance sufficient to allow the adhesive lines 16a, 16bto be applied to the vane material between the longitudinal edge of thevane material and the score-compressed line.

A structure similar to that shown in FIG. 12 can also be produced usinga relatively soft vane material, if desired. In this embodiment, astiffening agent is printed onto the vane material in the centralportion thereof to provide flatter vanes. The longitudinal edges of thevane material are left free of stiffening agent and the required hingepoints are formed at the longitudinally extending edges of the printedon stiffening agent. The adhesive lines are applied to the longitudinaledges of the vane material, which longitudinal edges have been left freeof stiffening agent.

According to another embodiment of the present invention, the vanes areformed of a black-out laminate material to maximize the room darkeningeffect of the window covering when the vanes are oriented in the closedposition. A suitable black-out laminate material is a three ply laminatecomprising a polyester film such as MYLAR sandwiched between two layersof a spun bonded or spun laced polyester nonwoven material. Black-outlaminates of this type are generally known in the art and havepreviously been used in other types of window coverings. Such a threeply laminate has, by virtue of its construction, a greater stiffnessthan most single ply materials. Accordingly, score-compressed hingepoints, such as those shown in FIG. 12, could be provided in theblack-out laminate vane material if necessary.

Alternatively, to produce a window covering of the present inventionhaving a maximized room darkening effect, only a stiffened centralportion of the vanes is formed from a black-out laminate material. Thelongitudinal edges of the vanes are left free of the black-out laminateto provide the required hinge points and flexibility along the edges ofthe vanes. When the black-out laminate is provided only on the centralportion of the vanes, it is desirable to space the vanes closer togetherthan described above in order to ensure that the black-out laminatedcentral portions overlap when the window covering is closed, for maximumroom darkening effect. For example, for a 2.5 inch wide vane with a 11/2inch wide black-out laminated central portion, the overlap of the vanesis preferably about 11/4 inch.

Another possible vane material is vinyl or a laminate of a nonwovenmaterial and a vinyl material. Generally, vinyl materials and laminatesof nonwoven material and a vinyl material provide an increased roomdarkening effect but are soft enough that score-compressed hinge pointsare not required. Of course, score-compressed hinge points could beprovided if necessary.

As discussed with respect to the first and second sheer fabrics of thewindow covering, when two woven fabrics are viewed in an overlayingrelationship, an interference pattern or moire effect can result. When anon-woven fabric is used for the vane material, the problem of a moireeffect in the window covering when it is closed is avoided. In someinstances, however, it may be desirable to use a woven or knit materialfor the vane material. A basic woven material will give a moire effectbecause this type of material has a very ordered orthogonal surfacestructure. To avoid a moire effect when the window covering having awoven or knit vane material is in the closed position, a crepe wovenmaterial can be used as the vane material because crepe woven materialshave a much more randomly oriented surface structure. Alternatively, thesurface of the woven or knit material can be altered to randomize thesurface fibers, for example, by sanding, napping or calendarizing.

Window coverings having first and second sheer fabrics and vanes ofvarious colors, and combinations of colors are contemplated within thescope of the present invention. For example, to provide a moretransparent window covering in the open position, dark sheer materialcan be used for the first and second sheer fabrics because dark colorsreflect less light than lighter colors. Similarly, white or lightcolored sheer materials provide a more translucent effect when thewindow covering is open.

The vanes may be the same color or a different color than the first andsecond sheer fabrics. A problem of glue line show-through has beenexperienced, however, when the vane material is a dark color and thefirst and second sheer fabrics are of a considerably lighter color orwhite. To overcome the problem of a dark glue line showing through alight colored sheer material when the vane is adhesively bonded to thefirst or second sheer fabric of the inventive window covering, a smallamount of whitener, about 0.5 to 1.0% by weight, is added to theadhesive before it is applied to the vane material. A particularlysuitable whitener is titanium dioxide. The addition of this whiteningpigment to the adhesive eliminates the problem of dark colored gluelines being visible in a window covering wherein a dark colored vane isadhesively bonded to a lighter colored sheer fabric.

The description of the preferred embodiments contained herein isintended in no way to limit the scope of the invention. As will beapparent to a person skilled in the art, modifications and adaptationsof the structure, method and apparatus of the above-described inventionwill become readily apparent without departure from the spirit and scopeof the invention, the scope of which is defined in the appended claims.

What is claimed is:
 1. A window covering comprising a first sheet ofrelatively translucent material, a second sheet of relativelytranslucent material disposed parallel to said first sheet, and aplurality of relatively opaque strips of material, each strip havingedge portions bonded to said first sheet and said second sheet,respectively, whereby central portions of said strips form vanes which,in a first closed position of said window covering are substantiallyplanar and extend substantially parallel to the first and second sheetseffective at least partially to block transmission of light and, in asecond open position of said window covering, extend generallytransverse to said first and second sheets, effective to transmit lightbetween said vanes, wherein said first and second sheets have adifferent physical appearance, wherein, said first and second sheets areeach sheer fabrics formed of threads defining interstices therebetween,the interstices of one sheet being of a different size and/or shapeand/or of a different orientation from those of the other sheet suchthat when the sheets are in overlying relation in the window coveringthe appearance of a moire effect is avoided when light is viewed throughboth the fabric sheets.
 2. A window covering according to claim 1,wherein the strips are formed of a fabric having threads defininginterstices therebetween, which are of a different size and/or shapeand/or orientation from the interstices of said sheets of fabric,whereby the appearance of a moire effect is avoided when said stripsextend parallel thereto in the first closed position of said windowcovering.
 3. A window covering according to any preceding claim, whereinone face of each vane is bonded to the first sheet and the opposite faceof each vane is bonded to the second sheet.
 4. A window coveringaccording to claim 3, wherein the portions of the strips between thebonded edge portions and the central portions form smoothly curvingportions, when the window covering is in its second open position.
 5. Awindow covering according to claim 4, wherein said strips have adequateresilience to tend to bias said fabrics towards said first closedposition.
 6. A window covering according to either of claim 4, whereinsaid strips are provided with reversely curving portions.
 7. A windowcovering according to claim 6, wherein the window covering furtherincludes an adhesive for bonding said edge portions to said first sheetand said second sheet.
 8. A window covering according to claim 7,wherein the adhesive is a hot-melt adhesive.
 9. A window coveringcomprising a first relatively translucent sheet of material, a secondrelatively translucent sheet of material disposed parallel to said firstsheet, and a plurality of flexible strips of relatively opaque materialhaving edge portions bonded to said first sheet and said second sheet,respectively, whereby central portions of said strips form vanes which,in a first closed position of said window covering are substantiallyplanar and extend substantially parallel to the first and second sheetseffective to at least partially block transmission of light and, in asecond open position of said window covering extend generallytransversely to said first and second sheets so as to effectivelytransmit light between said vanes, said strips having opposite faceswith one face of each vane being bonded to the first sheet and the otherface of each vane being bonded to the second sheet, the portions of thestrips between the bonded edge portions forming smoothly curvingportions so that the vanes are of generally S-shaped cross sectionalconfiguration when the window covering is in its second open position.10. A window covering according to claim 9, wherein said strips haveadequate resilience to tend to bias said fabric towards said firstclosed position.
 11. A window covering according to claim 9, wherein thewindow covering further includes an adhesive for bonding said edgeportions to said first sheet and said second sheet.
 12. A windowcovering according to claim 11, wherein the adhesive is a hot-meltadhesive.
 13. A window covering according to claim 9, wherein in saidfirst closed position adjacent strips partially overlap.
 14. A windowcovering according to claim 9, wherein said first and second sheets areeach plastic material sheets.
 15. A window covering according to claim9, wherein the front and rear sheets have a different physicalappearance to avoid the moire effect.
 16. A window covering according toclaim 15, wherein one of said first and second sheets is an open fabrichaving threads defining interstices therebetween and the other of saidsheets is a non-woven sheet material.
 17. A window covering according toclaim 15, wherein said first and second sheets are each open knitted orwoven fabrics formed of threads defining interstices therebetween, andinterstices of one sheet being of a different size and/or shape and/orof a different orientation from those of the other sheet, such that whenthe sheets are in overlying relation in the window covering, theappearance of a moire effect is avoided when light is viewed throughboth of the fabric sheets.
 18. A window covering according to either ofclaims 9 or 17, wherein the strips are formed of a fabric having threadsdefining interstices therebetween which are of a different size and/orshape and/or orientation from the interstices of said fabric sheets,whereby the appearance of a moire effect is avoided when said stripsextend parallel thereto in the first closed portion of said windowcovering.
 19. A window covering according to either of claims 9 or 17,wherein one face of each vane is bonded to the first sheet and theopposite face of each vane is bonded to the second sheet.
 20. A windowcovering according to claim 9, wherein said strips are made of amaterial having a softness such that when the material is allowed tohang off the edge of a horizontal surface a distance equal to the widthof a strip, the material will hang substantially vertically.
 21. A lightcontrol window covering comprising a first relatively translucent sheetof material, a second relatively translucent sheet of material disposedparallel to said first sheet, a plurality of strips of relatively opaquematerial affixed to said first and second sheets of material, each striphaving oppositely directed faces and edge portions, and an adhesivewhich was applied to opposite edge portions on opposite faces of eachstrip prior to its affirmation to said sheets whereby opposite edgeportions of the strips are adhesively bonded to said first sheet andsaid second sheet, respectively, and whereby central portions of saidstrips form vanes which, in a first closed position of said windowcovering are substantially planar and extend substantially parallel tothe first and second sheets effective at least partially to blocktransmission of light and, in a second position of said window coveringextend generally transverse to said first and second sheets, effectiveto transmit light between said vanes, wherein, said first and secondsheets are each open sheer fabrics having threads defining intersticestherebetween, the interstices of one sheet being of a different sizeand/or shape and/or of a different orientation from those of the othersheet, such that when the sheets are in overlying relation theappearance of a moire effect is avoided when light is viewed throughboth of the fabric sheets.
 22. A window covering according to claim 21,wherein in said first closed portion adjacent vanes partially overlap.23. A window covering according to either of claims 21 or 22 wherein theadhesive is a hot-melt adhesive.
 24. A window covering according toclaim 23, wherein said first and second sheets are each plastic materialsheets.
 25. A window covering according to claim 24, wherein one of saidfirst and second sheets is an open fabric having threads defininginterstices therebetween and the other of said sheets is a non-wovensheer material.
 26. A window covering according to claim 21, wherein thestrips are formed of a fabric having threads defining intersticestherebetween, which are of a different size and/or shape and/ororientation from the interstices of said fabric sheets, whereby theappearance of a moire effect is avoided when said strips extend parallelthereto in the first closed position of said window covering.
 27. Awindow covering according to claim 21, wherein said strips have adequateresilience to bias said fabrics towards said first closed position. 28.A window covering according to claim 27, wherein said strips areprovided with reversely curving portions.
 29. A window coveringaccording to claim 21, wherein said strips were affixed to said firstand second sheets by sequentially tack bonding said strips to the firstand second sheets, subsequently raising the temperature at the locationof the tack bonds to melt the glue, then lowering the temperature at thetack bonds to set the adhesive.